One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,405,693. This method presents a means to control electromagnetically actuated valves that may reduce exhaust noise. The approach attempts to reduce exhaust noise by staggering the opening timing of exhaust valves. This may reduce exhaust noise since cylinder pressure is restrained by initially releasing exhaust pressure through a single valve, thereby slowing the discharge of cylinder pressure into the exhaust manifold. The description also mentions that the method can be used to control intake valves by staggering the opening of two or more valves.
The above-mentioned method can also have several disadvantages. In particular, the approach requires two or more valves to regulate flow into or out of a cylinder. For engines with less than two intake and/or exhaust valves, the method may have reduced utility. For example, for a three valve, variable displacement engine (e.g., combusting an air-fuel mixture in four cylinders of an eight cylinder engine), having two intake valves and one exhaust valve, the method may not be effective for reducing exhaust manifold noise. Since the method relies on staggered opening of two valves to restrain flow into or out of the cylinder, the method may not be performed, in this example, to control exhaust gases since only one exhaust valve is present. Also for this example, operating the engine in a variable displacement mode can further increase engine exhaust noise that the method may not be capable of reducing since only a single exhaust valve is present.
In addition, depending on the engine operating region, multiple valves may not be necessary to improve engine breathing and power output. Therefore, adding an additional valve for the sole purpose of reducing engine noise may not make economic sense.
Furthermore, the above-mentioned method may increase engine pumping work in combusting cylinders of an engine if exhaust and/or intake valve timing is staggered. Pumping work can be increased by restraining flow into or out of a cylinder. Consequently, the fuel economy may decrease when valves are operated in this manner.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of electromechanical valve control that offers substantial improvements.